This invention relates to an automotive electronic control unit, particularly to a sealing structure of an electronic control circuit.
A conventional electronic control unit (hereinafter abbreviated as a control unit) for an engine or automatic transmission has been placed in the car interior. As the control unit grows bigger in the car interior, however, it has been requested that the control unit is placed outside the car interior. If the control unit is far away from objects to be controlled, wirings and connections become complicated and this increases the wiring cost. To improve this, it has been requested to integrate the control unit in the object to be controlled, more specifically, to make the control unit into a module.
In other words, it is necessary to place the control unit for the engine in the engine room or preferably on the engine body and similarly to place the control unit for the automatic transmission directly on the transmission body or inside the automatic transmission.
However, such places are in a severe temperature environment (−40 to 130° C.) and may be exposed to water, engine oil or AT oil (automatic transmission oil). Therefore, the control unit must be made by mounting electronic parts on a substrate having both heat resistant and heat-radiating characteristics such as a ceramic substrate and packaging them in a completely hermetic casing.
Judging from reliability and heat radiating ability, a metallic hermetic casing can be generally nominated, but it is hard to be adopted because of a high production cost. To solve this problem, Japanese Laid-Open Patent Publication No. Hei 06-61372 discloses, for example, a transfer-mold sealing structure which is a time-proven cheap and reliable semiconductor packaging technology.